The proposed research is intended to characterize the nature of the effect of heavy metals such as lead, mercury and cadmium on the function of the vertebrate retina. Although other retinal neurons will be examined, the work will emphasize the physiology of the photoreceptors with the object of determining the sites which are sensitive to heavy metals. Towards this end we will employ both extracellular and intracellular techniques of electrical recording to examine the influence of heavy metals on receptor potential amplitude, membrane potential and membrane resistance. Spectrophotometric measurements will allow us to monitor the effect of heavy metals on visual pigment regeneration. Standard radioisotope methodology will be used to observe any heavy metal involvement with ionic fluxes. Liposomes will be employed to aid in determining whether or not the effect of the heavy metals is exerted on the interior or the exterior of the photoreceptor. The experiments outlined in the proposal will tell us whether or not the heavy metals affect the visual pigments, the inside of the cell as opposed to the outside, the cell membrane, rapid dark adaptation mechanisms as well as potential generating mechanisms, or transduction processes which are dependent on calcium and/or zinc.